a) Field of the Invention
The invention is directed to a closure device for closing an opening in a wall in a vacuum-tight manner comprising a closure plate which, for the purpose of closing the closure device, is displaceable from an open position, in which the opening is released, to an intermediate position, in which it covers the opening but is raised from the wall, into a closed position in which it covers the opening and contacts the wall and, for the purpose of opening the closure device, is displaceable from its closed position to its intermediate position into its open position, a carrying unit which carries the closure plate and which has at least one longitudinal piston-cylinder unit by means of which the closure plate can be displaced in a closing direction from its intermediate position into its closed position and in an opening direction from its closed position into its intermediate position and which has a closing cylinder space for applying pressure to a closing piston surface by means of pressure gas in order to exert a force acting in closing direction and an opening cylinder space for applying pressure to an opening piston surface by means of pressure gas in order to exert a force acting in opening direction, a base unit which carries the carrying unit and has at least one transverse piston-cylinder unit by which the closure plate is displaceable in a closing direction from its open position to its intermediate position and in an opening direction from its intermediate position into its open position and which has a closing cylinder space for applying pressure to a closing piston surface by means of pressure gas in order to exert a force acting in closing direction and an opening cylinder space for applying pressure to an opening piston surface by means of pressure gas in order to exert a force acting in opening direction, wherein the closing cylinder space of the at least one longitudinal piston-cylinder unit is connected to the closing cylinder space of the transverse piston-cylinder unit or at least one of the transverse piston-cylinder units by means of a closing pressure gas channel, and the opening cylinder space of the at least one longitudinal piston-cylinder unit is connected to the opening cylinder space of the transverse piston-cylinder unit or at least one of the transverse piston-cylinder units by means of an opening pressure gas channel.
b) Description of the Related Art
A closure device of the type mentioned above is known from U.S. Pat. No. 6,056,266 A. To close the closure device, the closing cylinder spaces of the transverse and longitudinal piston-cylinder units are acted upon by pressure. However, the opening cylinder spaces are connected to atmospheric pressure. To open the closure device, the closing cylinder spaces and the opening cylinder spaces of the piston-cylinder units are acted upon by pressure gas, e.g., compressed air. Further, the closing piston surface is smaller than the respective opening piston surface in the transverse piston-cylinder unit as well as in the longitudinal piston-cylinder unit. This is achieved in the transverse piston-cylinder unit by a dual-action piston, wherein a guide rod having a greater diameter than the piston rod is arranged on the side of the piston located opposite from the piston rod. Two single-action pistons which have different diameters and are arranged in two portions of the cylinder bore hole which have different diameters are provided in the longitudinal piston-cylinder unit. A 3/2-way valve is used for switching between the open state of the closure device and the closed state of the closure device.